Method for detecting loss or undervoltage condition of phase of electric converter unit, conveyor control unit, and conveyor system

Abstract

A method for detecting a loss or an undervoltage condition of phase of an electric converter unit, wherein the method comprises: determining an extremum value, such as a maximum and/or a minimum value, of a phase voltage of the electric converter unit for at least one fundamental period of the phase voltage, and comparing the extremum value to a first threshold value, and if, based on the comparison, a first threshold criterion related to the first threshold value is satisfied, then determining the loss or the undervoltage condition of phase.

The invention claimed is: 
     
       1. A method for detecting a loss or an undervoltage condition of phase of an electric converter unit, wherein the method comprises:
 determining an extremum value, including a maximum and/or a minimum value of a phase voltage of the electric converter unit for at least one fundamental period of the phase voltage, and 
 comparing the extremum value to a first threshold value, and if, based on the comparison, a first threshold criterion related to the first threshold value is satisfied, then 
 determining the loss or the undervoltage condition of phase. 
 
     
     
       2. The method of  claim 1 , wherein the determination of the extremum value comprises removing an average value or a DC component of the phase voltage during the at least one fundamental period from the extremum value. 
     
     
       3. The method of  claim 2 , wherein the determination of the extremum value comprises determining the maximum value and the minimum value of the phase voltage for the at least one fundamental period of the phase voltage, and calculating the average value based on the maximum value and the minimum value. 
     
     
       4. The method of  claim 2 , wherein the first threshold value is less than 50 percent of a nominal amplitude of the phase voltage. 
     
     
       5. The method of  claim 1 , wherein the determination of the extremum value comprises determining the maximum value and the minimum value of the phase voltage for the at least one fundamental period of the phase voltage, and calculating the average value based on the maximum value and the minimum value. 
     
     
       6. The method of  claim 5 , wherein the first threshold value is less than 50 percent of a nominal amplitude of the phase voltage. 
     
     
       7. The method of  claim 1 , wherein the first threshold value is less than 50 percent of a nominal amplitude of the phase voltage. 
     
     
       8. The method of  claim 1 , wherein the satisfying the first threshold criterion includes satisfying the first threshold criterion during at least two, consecutive fundamental periods. 
     
     
       9. The method of  claim 1 , comprising performing the method steps also for one or several other phase voltages. 
     
     
       10. The method of  claim 1 , comprising determining if the electric converter unit has a current path to a main power supply. 
     
     
       11. The method of  claim 1 , wherein the extremum value and/or the absolute values of phase currents are determined by a voltage or current measurement device or devices, respectively, arranged to an input phase or phases of the electric converter unit. 
     
     
       12. The method of  claim 1 , wherein the extremum value and/or the absolute values of phase currents are determined with a sampling rate of one sample in a millisecond. 
     
     
       13. A conveyor control unit comprising a processing unit and a memory, wherein the conveyor control unit is configured to perform a method according to  claim 1 . 
     
     
       14. A conveyor system, such as an elevator system, an escalator, or a moving walkway, comprising a conveyor moving steps or track, wherein the conveyor system comprises the conveyor control unit of  claim 13 . 
     
     
       15. A method for detecting a loss or an undervoltage condition of phase of an electric converter unit, the method comprising:
 determining an extremum value, including a maximum and/or a minimum value, of a phase voltage of the electric converter unit for at least one fundamental period of the phase voltage, 
 comparing the extremum value to a first threshold value, and if, based on the comparison, a first threshold criterion related to the first threshold value is satisfied, then determining the loss or the undervoltage condition of phase, 
 determining absolute values of phase currents of the electric converter unit during at least one fundamental period, 
 integrating the absolute values of phase currents with respect to time or determining ampere-second balances of the phase currents, 
 comparing the integrated absolute values or the ampere-second balances to a second threshold value, and if, based on the comparison, a second threshold criterion related to the second threshold value is satisfied, then 
 comparing the integrated absolute value or the ampere-second balance of one of the phase currents to the integrated absolute value or the ampere-second balance of one or several other phase currents, and, if, based on the comparison, a third threshold criterion is satisfied, then 
 determining the loss of the phase. 
 
     
     
       16. The method of  claim 15 , comprising performing the comparison of the integrated absolute value or the ampere-second balance also for the one or several other phase currents. 
     
     
       17. The method of  claim 15 , wherein the satisfying of the second threshold criterion relates to any one of the integrated absolute values or the ampere-second balances being higher than or equal to the second threshold value. 
     
     
       18. The method of  claim 15 , wherein the satisfying of the third threshold criterion relates to the integrated absolute value or the ampere-second balance of one of the phase currents being less than the integrated absolute value or the ampere-second balance of one other phase current. 
     
     
       19. The method of  claim 18 , wherein the satisfying of the third threshold criterion relates to the integrated absolute value or the ampere-second balance of one of the phase currents being less than 50 or 25 percent of the integrated absolute value or the ampere-second balance of the one other phase current. 
     
     
       20. The method of  claim 15 , wherein the satisfying of the second threshold criterion and/or the third threshold criterion includes satisfying the criterion during at least two consecutive fundamental periods.